Method for photoelectrochemical polishing of silicon wafers

Abstract

A method is provided for photochemical polishing of a silicon wafer using electromagnetic waves within the spectrum of 150 to 2000 nanometers wavelength. A photochemical polishing apparatus is also disclosed in which the electromagnetic waves are provided by a waveguide in close proximity to the surface of a silicon wafer electrode.

What is claimed is: 
     
       1. A method for photoelectrochemical polishing of a silicon wafer comprising: placing said silicon wafer in a photoelectrolytic cell as an electrode and, with an electrolyte comprising a conductive ion as a nucleophilic or an electrophilic species, applying a potential to said silicon wafer electrode while irradiating the surface of said silicon wafer electrode with electromagnetic waves within the spectrum of 150 to 2000 nanometers wavelength; wherein said photoelectrolytic cell comprises: (a) a wave guide which provides evanescent radiation of predetermined wavelength(s) in close proximity to the surface of said silicon wafer electrode and (b) an electrolyte, in the space between said silicon wafer surface and said wave guide, having an absorption coefficient for said predetermined wavelength(s) such that said evanescent radiation is reduced to at most 10% of its initial intensity over a path length of 2 microns.   
     
     
       2. A method according to claim 1 wherein said electrolyte comprises ammonium fluoride at about 0.5 molar to 8 molar concentration in water. 
     
     
       3. A method according to claim 2 wherein said electrolyte further comprises a surfactant at about 0.1% to about 5% by weight. 
     
     
       4. A method according to claim 3 wherein said surfactant is piperonal.